This invention relates to a process for the production of urethanes (carbamic acid esters or carbamates). More specifically, it relates to a process in which primary amines are reacted with organic hydroxyl compounds and carbon monoxide in the presence of an oxidizing agent and in the presence of a catalyst system. The catalyst system includes at least one noble metal or at least one noble metal compound, and a quinoid compound or compound capable of being converted into a quinoid compound.
Generally, organic isocyanates are commercially produced by reacting the corresponding amine with phosgene. However, due to the high chlorine demand and the high energy costs involved in the production of phosgene, considerable efforts have been exerted to find a commercially workable method for producing organic isocyanates in which there is no need to use phosgene. In one such method, primary amines are reacted with carbon monoxide, organic hydroxyl compounds and an oxidizing agent (such as air or an organic nitro compound) to form the corresponding urethanes; the urethanes thus formed are then split into isocyanates and compounds containing hydroxyl groups. This phosgene-free process for producing urethanes is described in German Offenlegungsschrift No. 2,910,132 and in German Offenlegungsschrift No. 2,908,251 (.dbd.EP-OS No. 16346 or U.S. Ser. No. 125,394 filed Feb. 27, 1980). In the process described in German Offenlegunggschrift No. 2,908,251, primary amines are catalytically oxycarbonylated by reaction with carbon monoxide, organic hydroxyl compounds, an oxidizing agent which is either molecular oxygen or a nitro compound and a catalyst. The disclosed catalyst is, from 1 to 5 weight % (based on the mixture as a whole,) of chloride-containing, inorganic solids which are largely insoluble in the reaction mixture used in combination with a noble metal catalyst. This latter process, however, is disadvantageous in that the high content of chloride-containing compounds causes corrosion problems in the process apparatus. Additionally, the fact that the inorganic catalyst components are substantially insoluble seriously affects the commercial practicability of the known process.